Kerala SSLC Class 9 Solutions for biology – The Chemical Changes of Food (English Medium)
Page No. 13:
Plants prepare food using sunlight.
But animals cannot do this. If so, where do animals get their food from?
Animals cannot prepare their own food from sunlight like plants. They get their food from plants or other animals, i.e. primary consumers which directly feed on plants.
For what purposes do animals use the food that is produced by plants through photosynthesis?
Animals use food produced by plants through photosynthesis for the following purposes:
- To obtain energy
- To grow
- To replace worn out cells
Examine the figure, find out the important nutrients in the food items given below and complete the table.
Page No. 14:
How does the body utilise these nutrients contained in the food items for various purposes?
- Various nutrients present in food are digested by the human body and broken into simpler units.
- These simpler units of nutrients are transported to different body cells through blood.
- They are then absorbed by the body cells and again assimilated to build complex molecules according to the energy needs of the body.
Prepare a note on the various nutrients contained in food, their sources, functions, and their simpler units.
Page No. 16:
Complete the illustration given below on the basis of your understanding about the nutrients.
How do these factors present in the food materials get transformed into simpler units that can be utilized by the body? What happens to the food that we eat?
Factors present in food materials get digested by various enzymes present in the alimentary canal and get transformed into simpler units which can be used by the body.
Observe the figure, identify and label the parts.
Using the given figure find out the different parts of the alimentary canal through which food passes.
Different parts of the alimentary canal through which food passes:
- Small intestine
- Large intestine
Page No. 17:
What happens to the food in the mouth?
In the mouth, the food is cut into pieces, torn and chewed to small particles with the help of teeth. The tongue helps small food particles to mix with saliva and form a soft mass of food which is swallowed.
What are the parts in the mouth that help to convert food into small particles?
Different types of teeth help to convert food into small particles. Incisors help in cutting, canines help in tearing and premolar and molars help in chewing or grinding food.
Page No. 18:
How do the tongue and the teeth help in the process of mechanical digestion in the mouth?
Teeth help to convert food into small particles.
Incisors help in cutting, canines help in tearing and premolar and molars help in chewing or grinding food.
The tongue helps in mixing and chewing of food in the mouth.
Thus, the tongue and the teeth help in the process of mechanical digestion in the mouth.
Is there any difference in the number of teeth in children and adults?
In children, there are 28 teeth which are the first set of teeth. These 28 teeth fall. Four more teeth grow in humans on attaining adulthood. These teeth are known as wisdom teeth. Hence, adult humans have a set of 32 teeth.
How many types of teeth are present in the human mouth? What are their functions?
Four types of teeth are present in the human mouth:
Functions of different types of teeth:
- Incisors – cutting food
- Canines – tearing food
- Premolars and molars – chewing food
What is the special feature of teeth that helps to convert food into small particles?
Human teeth are covered with the hardest substance in the human body called enamel. Enamel makes teeth hard and strong, thus helping to convert even hard food substances into small particles.
Why do we say that food should be chewed well?
Chewing food well helps break down food particles properly and the mixing of saliva with the food particles creates a food bolus which is soft and lubricated. Hence, it can easily slide down to the oesophagus.
Is mechanical digestion the only process that takes place in the mouth?
Teeth in the mouth carry out mechanical digestion of food.
Besides mechanical digestion, enzymes present in saliva help in the chemical digestion of starch present in the food.
When food reaches the mouth more saliva is secreted from the salivary glands. The saliva mixes food to make the process of chewing easier. Does saliva perform any other function?
Components of saliva help in digestion in several ways:
- Mucus conducts food smoothly through the oesophagus.
- Salivary amylase converts starch to maltose.
- Lysozymes present in saliva destroy microorganisms present in food.
Page No. 19:
Is the stomach only a storage organ?
Food is stored in the stomach, but the constant movement of the walls of the stomach constantly churns food.
Hence, partial digestion of food also takes place in the stomach.
Find out what are the changes occurring to the food in the stomach.
Following changes occur in food in the stomach:
- Proteins are converted to peptones in partial digestion.
- Microorganisms present in food are destroyed by the action of HCl.
- Food is churned and mixed well.
Page No. 20:
What is the role of liver in the process of digestion?
Role of the liver in digestion:
- The liver secretes bile juice in the small intestine.
- Bile helps to change the pH of food from the stomach from its acidic nature to its basic nature.
- Bile also helps to convert lipids into smaller particles.
What are the simple units that are formed in the small intestine as a result of digestion?
As a result of digestion, the following simple units are formed in the small intestine:
- Maltose (from starch)
- Peptides (from proteins)
- Fatty acids and glycerol (from fats and lipids)
- Amino acids (from peptides)
- Glucose, fructose, galactose (from carbohydrates)
List out the nutrients in our common diet like gruel, peas and pappads.
Find out at which parts of the alimentary canal, each of these is digested and what are the simpler components of each of these after digestion.
Page No. 21:
Analyse the similarities and differences in food habits and digestive processes of amoeba, hydra and tapeworm.